7. What is AOT compilation? Why Use in Angular 2?

 AOT compilation stands for “Ahead of Time compilation” and it are used to compiles the angular components and templates to native JavaScript and HTML during the build time instead of run-time. The compiled HTML and JavaScript are deployed to the web server so that the compilation and render time can be saved by the browser. It is the big advantage to improve the performance of applications.

Advantages of AOT -

1. Faster download: - The Angular 2 app is already compiled so it is faster.
2. Faster Rendering: - If the app is not AOT compiled and the compilation process happens in the browser once the application is fully loaded. This has a wait time for all necessary components to be downloaded and then the time taken by the compiler to compile the app. With AOT compilation, this is optimized.
3. Lesser Http Requests: - It is supporting to the lazy loading. Actually, lazy loading is great concepts for sending HTTP request to the server. It is minimise the multiple requests for each associated html and css, there is a separate request goes to the server.
4. Detect error at build time: - In Angular 2, the compilation happens beforehand and most of the errors can be detected at the compile time and this process providing us a better application’s stability.

Disadvantages of AOT -
1. AOT only works only with HTML and CSS and not for other file types. If required other file types that time we will need to follow the previous build step.
2. We need to maintain AOT version of bootstrap file.
3. We need to clean-up step before compiling.